Optocouplers contain at least one optical emitter device which is optically coupled to an optical receiver device through an optically transmissive medium. This arrangement permits the passage of information from one electrical circuit that contains the optical emitter device to another electrical circuit that contains the optical receiver device. A high degree of electrical isolation is maintained between the two circuits. Because information is passed optically across an insulating gap, the transfer is one way. For example, the optical receiver device cannot modify the operation of a circuit containing the optical emitter device. This feature is important because, for example, the emitter may be driven by a low voltage circuit using a microprocessor or logic gates, while the output optical receiver device may be part of a high voltage DC or AC load circuit. The optical isolation also prevents damage to the input circuit caused by the relatively hostile output circuit.
A common optocoupler package format is the dual-in-line package or DIP. This package is widely used to house integrated circuits and is also used for conventional optocouplers. Various versions of optocoupler DIP packages having 4, 6, 8 or 16 pins are commonly manufactured.
FIG. 1 shows a cross section of a conventional optocoupler DIP package 10. The illustrated optocoupler 10 includes a lead frame 24 comprising leads 24(a), 24(b) (i.e., pins). An optical emitter device 12 is mounted on one lead 24(a). An optical receiver device 14 is mounted on the other lead 24(b). The optical receiver device 14 generates an electrical signal after receiving light generated by the optical emitter device 12. The optical emitter device 12 is electrically coupled to the lead 24(a) through its bottom surface, and to another lead (not shown) via a wire 11. Similarly, optical receiver device 14 is electrically coupled to the lead 24(b) through the bottom surface and to another lead (not shown) via a wire 13. It will be recognized by those skilled in the art that the optical emitter device 12 operates with two electrical connections, an anode and a cathode. These connections are thus provided by the wire 11 and the lead 24(a). Similarly, optical receiver device 14 operates with two electrical connections, typically an emitter and a collector. These connections are provided by the wire 13 and lead 24(b). The optocoupler package 10 further includes an optically transmissive medium 16. A molding compound 18 encases the leadframe 24, optical emitter device 12, optical receiver device 14, and the optically transmissive medium 16.
A number of improvements could be made to the optocoupler package 10 shown in FIG. 1. For example, the optocoupler package 10 requires an expensive and time consuming overmolding process. In the overmolding process, the molding compound 18 encapsulates the other parts of the optocoupler package 10. In addition to the overmolding process itself, mold material removal processes (e.g., dejunk and deflash processes) are used to remove excess molding compound, thus adding to the time and expense of forming an optocoupler package. In addition, the tooling that is needed to create moldings of different “form factors” (e.g., 4, 6, or 8 pin packages) requires a significant capital investment. Accordingly, if the overmolding process could be eliminated, the time and costs associated with producing optocoupler packages could be reduced.
Other improvements to the optocoupler package 10 could also be made. The optocoupler package 10 is also prone to failure from thermal cycling. For example, the difference in the thermal expansion properties of the molding compound 18 and the optically transmissive medium 16 causes them to expand and contract at different rates when they are heated and cooled. The molding compound 18 and the optically transmissive medium 16 could potentially separate, thus resulting in a structurally weak package. Temperature cycling also produces stress at the points where the lead frame 24 exits the molding compound 18 (e.g., at point “A”). The stress can result in a broken or weakened lead frame 24. Also, the wires 11, 13 can sometimes pass through the optically transmissive medium 16 and the molding compound 18. Differences in the thermal expansion properties of the optically transmissive medium 16 and the molding compound 18 can induce stress in the wires 11, 13 and can cause them to break.
It would also be desirable to reduce the height of conventional optocoupler packages. The optocoupler package 10 shown in FIG. 1 is relatively high. For example, the net height of a typical DIP package is about 3.5 to about 4.0 mm. It would be desirable to reduce the height of the optocoupler package so that it has a lower profile. By doing so, smaller electronic components could be produced.
It would also be desirable to increase the functionality of the above-described package and also to reduce the costs associated with manufacturing the optocoupler package.
Embodiments of the invention address these and other problems, individually and collectively.